Английский язык. Сборник практических заданий по энергетике с ответами

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Text: Sound Еnergy.

Energy may take various forms — sound, chemical, and electrical energy, for example Sound consists of waves of alternate compression and rarefaction that transmit kinetic energy through a medium. If there is no medium, there is no sound; sound waves cannot pass through a vacuum. All sounds originate from vibrating objects, such as the vocal cords in the human throat, the skin of a drum, or the strings of a violin.

The vibrations are then passed on through a medium — most commonly air — until they strike the ear drum; the ear converts the vibrations into nerve impulses, which pass to the brain where they are interpreted as sounds. Microphones are the other most common instruments of sound waves into electrical signals.

Waves and sound. There are two types of waves in physics: longitudinal and transverse. Sound waves are of the longitudinal type — that is, their vibrations take place in the same direction as they travel.

Transverse waves are those in which the vibrations occur at right angles to the direction, in which the waves travel — as happens, for example, when a length of rope is moved regularly up and down to give it a wavelike appearance. Ocean waves and light waves also travel by transverse propagation.

Frequency and intensity. The frequency of a sound wave is the number of wavelengths that are completed in a given period of time.

The universal unit of measurement is the hertz (Hz), which represents one complete wavelength, or cycle, per second. The human ear is sensitive to sound in the frequency range from about 20 Hz. As people grow older, their ability to perceive high frequencies diminishes.

The intensity of sound is measured in terms of the amount of power that passes each second through a given area perpendicular to the direction of the sound wave. The intensity unit is the decibel (db).

Velocity. Sound can be transmitted by any medium — gas, liquid, or solid — and all sound waves travel at a constant velocity through any given medium at a constant temperature. But depending on their elasticity and density, some mediums transmit waves faster than others.

The velocity of sound is affected by temperature; as the temperature increases, the medium expands. Its density decreases, with the result that the velocity of sound increases.

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